Tetrathionate

File:Tetrathionate-ion-2D.png

The structure of the tetrathionate anion

The tetrathionate anion, S₄O₆²⁻, is a sulfur oxoanion derived from the compound tetrathionic acid, H₂S₄O₆. Two of the sulfur atoms present in the ion are in oxidation state 0 and two are in oxidation state +5. Alternatively, the compound can be viewed as the adduct resulting from the binding of S₂²⁻ to SO₃. Tetrathionate is one of the polythionates, a family of anions with the formula [S_n(SO₃)₂]²⁻. Its IUPAC name is (sulfonatodisulfanyl)sulfonate, the name of its corresponding acid is (sulfodisulfanyl)sulfonic acid. The Chemical Abstracts Service identifies tetrathionate by the CAS Number 15536-54-6.

Formation

Tetrathionate is a product of the oxidation of thiosulfate, S₂O₃²⁻, by iodine, I₂:

2S₂O₃²⁻ + I₂ → S₄O₆²⁻ + 2I⁻

Structure

Tetrathionate's structure can be visualized by following three edges of a cube, as in the diagram below. The structure shown is the configuration of S₄O₆²⁻ in BaS₄O₆·2H₂O and Na₂S₄O₆·2H₂O. Dihedral S-S-S-S angles approaching 90° are common in polysulfides.

Detailed structure of the tetrathionate ion Ball-and-stick model of the tetrathionate ion

Compounds

Compounds containing the tetrathionate anion include sodium tetrathionate, Na₂S₄O₆, potassium tetrathionate, K₂S₄O₆, and barium tetrathionate dihydrate, BaS₄O₆·2H₂O.

Properties

As other species of sulfur at intermediate oxidation state, such as thiosulfate, tetrathionate can be responsible for the pitting corrosion of carbon steel and stainless steel.

Tetrathionate has also been found to serve as a terminal electron acceptor for Salmonella Typhimurium, whereas existing thiosulfate in the lumen of mammals is oxidized by reactive oxygen species released by the immune system (mainly NADPH oxidase produced superoxide) to form tetrathionate. This aids in the growth of the bacterium, helped by the inflammatory response.

See also

• Corrosion
• Dithionite
• Polysulfides
• Thiosulfate